The present invention generally relates to a system and method for image processing of multiple images of an object. In particular, the present invention relates to a system and method for synchronizing corresponding landmarks among multiple images of an object.
Medical diagnostic imaging systems encompass a variety of imaging modalities, such as x-ray systems, computerized tomography (CT) systems, ultrasound systems, electron beam tomography (EBT) systems, magnetic resonance (MR) systems, and the like. Medical diagnostic imaging systems generate images of an object, such as a patient, for example, through exposure to an energy source, such as x-rays passing through a patient, for example. The generated images may be used for many purposes. For instance, internal defects in an object may be detected. Additionally, changes in internal structure or alignment may be determined. Fluid flow within an object may also be represented. Furthermore, the image may show the presence or absence of objects in an object. The information gained from medical diagnostic imaging has applications in many fields, including medicine and manufacturing.
One particular application for the information acquired from medical diagnostic imaging is in the diagnosis and treatment of cancer. Although there are many different kinds of cancer, they all share a common cause: an uncontrollable growth of abnormal cells. As most cancer cells grow and accumulate, they form a tumor. Medical diagnostic imaging allows various sections of the human body to be examined for cancerous cells and tumors.
A particular type of medical diagnostic imaging used in detecting cancerous growths is tomographic reconstruction. Tomographic reconstruction reconstructs tomographic images for two-dimensional and three-dimensional image scans. Tomographic reconstruction reconstructs an image from image data projections (such as x-ray projections) generated in an image acquisition system. Data from multiple projections are combined to produce an image representing an object. Often, two-dimensional slices are reconstructed from scans of a three-dimensional object. The two-dimensional slices may be combined to construct a three-dimensional image. These two or three dimensional images may be viewed by a physician, or other health care practitioners, in search of cancerous growths, for example.
However, not all forms of cancerous growths are easily detected using tomographic reconstruction. One such area is that of colorectal cancer. Excluding skin cancers, colorectal cancer is the third most common cancer diagnosed in both men and women in the United States. The American Cancer Society estimates that about 105,500 new cases of colon cancer (49,000 men and 56,500 women) and 42,000 new cases of rectal cancer (23,800 men and 18,200 women) will be diagnosed in 2003. Colorectal cancer is expected to cause about 57,100 deaths (28,300 men and 28,800 women) during 2003.
Colorectal cancers are thought to develop slowly over a period of several years. Most colorectal cancers begin as a polyp, a mass of tissue that grows into the center of the tube that makes up the colon or rectum. Once a cancer forms in these polyps, the cancer may grow into the center of the colon or rectum. The cancerous polyp will also grow into the wall of the colon or rectum where the cancer cells may grow into blood vessels. From these vessels, the cancer cells may then break away, spreading to other parts of the body.
Although colon cancer is the third most common cancer diagnosed and the second largest cause of cancer related death in the United States, it has been estimated that up to ninety percent of colon cancers may be prevented. Colonic polyps develop slowly and may take years before becoming cancerous. If polyps are found early, they may be removed before they develop into cancer, or if they are already cancerous, they may be removed before the cancer spreads. Thus, the one of the keys to preventing colon cancer is screening for potential cancerous polyps. The importance of screening is further magnified because most colonic polyps do not produce any symptoms, and nearly seventy-five percent of people who develop colon cancer have no risk factors for the disease, yielding no warning for the onset of cancer.
The American Cancer Society recommends that every person over the age of fifty be screened for colon cancer. They estimate that if everyone were tested, tens of thousands of lives could be saved each year. However, although colon cancer is the second largest cause of cancer related death, only forty percent of Americans who are at risk for the disease are currently screened as recommended. So few individuals are screened because people typically find the screening methods for colon cancer distasteful. For example, one screening method calls for testing the stool for blood. The blood screening method requires patients to collect stool samples at home to send to the doctor's office for testing. Another screening method, a colonoscopy, involves a bowel cleansing process which lasts about a day, followed by sedation and an examination of the colon with a five-foot-long probe. Due to the time consuming and invasive nature of a colonoscopy, many people choose not to have the colonoscopy.
Tomographic reconstruction of a colon has been advocated as a promising technique for providing mass screening for colorectal cancer. Tomographic reconstruction of a colon is often called a computed tomography colonography (CTC), also called a virtual colonoscopy. A virtual colonoscopy is a technique for detecting colorectal neoplasms by using a computed tomography (CT) scan of a cleansed and air-distended colon. The CTC scan typically involves two CT scans of the colon, a prone scan and a supine scan. A prone scan may include a patient lying face down, for example. Moreover, a supine scan may include a patient lying face up, for example. Both the prone and supine scans capture hundreds of images of a patient's abdomen forming a prone and supine image set. Each image is captured in 20-30 seconds, for example, which translates into an easier, more comfortable examination than is available with other screening tests. Usually, a CTC takes approximately ten minutes, and a person may return to work the same day. Thus, a system and method providing a quick, effective and friendly screening process would be highly desirable. There is a need for a method and system that increases early detection of cancerous polyps and other materials.
However, currently CTC is not a practical clinical tool for colon cancer screening. For CTC to be a practical procedure of screening for colon cancers, a technique should reduce the time for interpreting a large number of images in a time-effective fashion, and for detecting polyps and masses with high accuracy. Currently, however, interpretation of an entire CTC examination is time consuming. A typical CTC examination produces 150-300 axial CT images for each the supine and prone image sets, yielding a total of 300-700 images/patient. Studies show that a case interpretation time per patient is between 15 and 40 minutes even when the reading is done by experts in abdominal imaging. Thus a system and method that reduces CTC case interpretation time would be highly desirable.
In addition, the diagnostic performance of CTC currently remains vulnerable to perceptual errors. Several studies have reported a relatively low sensitivity, 40%-70%, for example, in the detection of polyps using a CTC examination. A low detection rate may result from the system and method used to display and view the images. Thus, an improved system and method used to display and view the images may improve the detection of cancerous growths.
As previously mentioned, a CTC examination involves two scans: a prone scan and a supine scan. Multiple scans may be obtained due to the elastic structure of the colon. That is, the colon is a flexible structure, much like an accordion, that changes shape based on body position. Portions of the colon that are visible in a prone view, may not be visible in a supine view, and vice versa, for example. Thus, in order to have an accurate representation of the colon, both a prone and supine scan should be conducted.
Another reason that performing two scans of the colon provides a more accurate representation than a single scan is that even though pre-exam procedures call for a bowel cleansing process, excess liquid or residual fecal matter within the colon may still be lingering during the exam. Because the excess material has a tendency to shift between a prone image set and a supine image set, target items or potential polyps may be observable in one image set and obscured in the other. Hence, both image sets must be compared and contrasted during a CTC case interpretation.
Often, both the prone and supine image sets are compared and contrasted simultaneously. Ideally, a particular portion of the colon in one set is searched for polyps, and then the corresponding portion of the colon in the second set is also reviewed for polyps. Each potential growth or polyp is scrutinized to determine whether it actually is a polyp or simply excess material. One method to distinguish excess material from a polyp is to compare corresponding locations of the colon in both the prone and supine image sets. Because the excess material tends to shift between a prone and supine image scan, the excess material seen in a particular location in one image set will usually be in a different location in the corresponding image set. However, polyps typically do not change location between the image sets. Thus, if a growth is in a particular location of the colon in both image sets, the growth may be a potential polyp.
Observing a similar growth in corresponding locations of the colon in both the prone and supine image sets facilitates a comparison analysis. Current systems and methods for viewing CTC prone and supine image sets do not link the image sets together. Unlinked images may create difficulty for a user when determining whether or not corresponding locations in the prone and supine image sets are being viewed. Hence, the user currently guesses if the portion of the colon being viewed in the prone image set is the same portion of the colon being viewed in the supine image set.
Guessing whether the portion of the colon being viewed in the prone image set is the same portion of the colon being viewed in the supine image set is very time consuming due to the manual, imprecise nature of the analysis. Forcing a user to guess at colon location accounts for an extremely long CTC case interpretation time per patient. A user spends a significant amount of time ascertaining whether the user is viewing corresponding locations of the colon in each of the prone and supine views. Even if a user thinks the user is viewing two corresponding locations of a colon, currently the user may not be certain. As is explained above, a long CTC case interpretation time currently makes clinical screening impracticable.
Also, rough estimation of corresponding locations provides for a highly inaccurate procedure for distinguishing excess material from potential cancerous growths or other objects. The low detection rate of detecting polyps using a CTC examination mentioned above is partially caused by a user's inability to determine whether the user is viewing corresponding locations of the colon in prone and supine views. As is explained above, the low detection rate currently makes clinical CTC screening impracticable.
Therefore, a need exists for a system and method which synchronizes corresponding locations of an object among multiple images. Such a system and method may be used to synchronize corresponding locations of prone and supine image sets of a CTC examination, for example, thereby reducing CTC case interpretation time and increasing detection rate of potentially cancerous polyps.